延續上一篇問題
建立滿足以下關係的Table Associations
- User can create a tag for a book.
- According to a given tag, return book list.
- According to a given book, return tag list.
這次只用一個Join Table但包含了3個FK來實作
建立4個Table
schema
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
|
create_table "books", force: :cascade do |t|
t.string "title"
end
create_table "tags", force: :cascade do |t|
t.text "label"
end
create_table "user_book_tags", force: :cascade do |t|
t.integer "user_id"
t.integer "book_id"
t.integer "tag_id"
end
create_table "users", force: :cascade do |t|
t.string "name"
end
|
其中user_book_tags包含了user_id, book_id, tag_id，3個Foreign key
設定Model Associations
User
1
2
3
4
|
class < ActiveRecord::Base
has_many :user_book_tags
has_many :tags, through: :user_book_tags
end
|
Book
1
2
3
4
|
class Book < ActiveRecord::Base
has_many :user_book_tags
has_many :tags, through: :user_book_tags
end
|
Tag
1
2
3
4
5
6
|
class Tag < ActiveRecord::Base
has_many :user_book_tags
has_many :users, through: :user_book_tags
has_many :books, through: :user_book_tags
end
|
UserBookTag
1
2
3
4
5
|
class UserBookTag < ActiveRecord::Base
belongs_to :user
belongs_to :book
belongs_to :tag
end
|
再來是在Rails Console裡測試
1
2
3
4
5
6
7
8
9
10
11
|
> User.create(name: "Tomo")
> Book.create(title: "Ruby")
> Tag.create(label: "good book")
> UserBookTag.create(user: User.first, book: Book.first, tag: Tag.first)
> User.first.tags
> Book.first.tags
> Tag.first.users
> Tag.first.books
|
與上一次的方法相比，少建立一個Table。
近期评论